JP2621049B2 - Valve system for 4-cycle engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a valve train for driving intake and exhaust valves of a four-stroke engine.

[Conventional technology]

In general, in a four-stroke engine mounted on a vehicle such as an automobile or a motorcycle, an intake / exhaust valve is disposed above a combustion chamber, and the valve train includes a cus shaft for operating the intake / exhaust valve. . When the camshaft is rotated by the power of the engine, the intake / exhaust valve is moved up and down at a predetermined timing by a cam having a unique cam profile formed on the camshaft, so that the mixture is sucked and the combustion gas is exhausted.

In the above-described conventional valve train, each of the intake and exhaust valves is always operated by a cam having the same cam profile. Therefore, the opening and closing of each valve set according to the engine speed is performed. The lift amount of the valve moved up and down by the timing and the rotation of the cam is always constant without fluctuation.

[Problems to be solved by the invention]

By the way, in the above-mentioned four-stroke engine mounted on a vehicle such as a motorcycle, it is required to obtain a high output within a wide rotation speed range from a low rotation speed range to a middle and high rotation speed range, that is, to obtain a wide power band. Have been.

However, in the above-described conventional valve train, each of the intake and exhaust valves is always operated by a cam having the same cam profile, so that the opening / closing timing of each valve and the lift amount of the valve are always constant without fluctuation. Therefore, the output characteristic of the engine is generally limited by the cam profile of the cam that operates the valve, and has an output characteristic having a peak value in a specific engine speed range, and therefore, from a low speed range to a middle / high speed range. Higher output could not be obtained in a wide speed range.

The present invention has been made in view of the above-described circumstances, and has been developed from a low rotation speed range to a middle rotation speed.
It is an object of the present invention to provide a valve apparatus for a four-cycle engine in which the output is improved within a wide rotation speed range over a high rotation speed range.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, a camshaft in which two types of cams having different cam profiles are formed adjacent to each other and at least one of the cams has a larger cam lift than the other cam. A first rocker arm disposed below a cam having a small cam lift among cams formed in the camshaft and directly in contact with a valve head for opening and closing a combustion chamber;
A second rocker arm, which is disposed below a cam having a large cam lift among the cams formed in the cam shaft and is engaged with the upper surface of the first rocker arm, is rotatably supported, and The part to be inserted into each support part of the first and second rocker arms and the part to be inserted into the support part of the second rocker arm has a larger diameter than the other part, and the center of the axis is the other part. A rocker shaft formed with an eccentric large diameter portion eccentric from the axis of the rocker shaft, and by rotating the rocker shaft by a predetermined angle in a low engine speed range, the eccentric large diameter portion of the rocker shaft allows the The supporter of the second rocker arm is moved downward relative to the supporter of the first rocker arm. The contact between the formed cam having a large cam lift and the second rocker arm is released, and the cam having the small cam lift is brought into contact with the first rocker arm, and the valve is set to have the small cam lift. By operating the cam according to the cam profile of the cam and rotating the rocker shaft by a predetermined angle in a middle / high rotation speed range, the support portion of the second rocker arm is moved to the first position by the eccentric large diameter portion. The cam is lifted to a position equivalent to the support portion of the rocker arm, thereby releasing the contact between the cam having a small cam lift and the first rocker arm, and separating the cam having a large cam lift and the second rocker arm. Abutting and operating the valve by following the cam profile of the cam with the large cam lift. There.

[Action]

According to the above-described valve gear, since the cam profile of the cam that operates the valve can be selected from two types according to each rotation range of the engine, the opening / closing timing of each valve and the lift amount of the valve can be adjusted by the engine rotation. An optimum value can be set according to the number range.

〔Example〕

Hereinafter, an embodiment of the valve train according to the present invention will be described in detail.

FIG. 1 is a conceptual perspective view of a main part showing a valve train 1 according to the present invention. The valve gear 1 is provided at two locations, one at each of the intake valve side and the exhaust valve side with respect to one cylinder.

The valve gear 1 has a camshaft 4 in which two types of cams 2 and 3 having different cam profiles are formed adjacent to each other, and first and second rocker arms 5 and 5 disposed below the camshaft 4. 6 and each supporting part of each rocker arm 5, 6
The rocker shaft 7 is inserted into 5a, 6a and rotatably supported by a bearing (not shown).

Of these, the cam 2 formed on the camshaft 4 has a cam profile (hereinafter referred to as low speed) having a cam profile suitable for improving the output of the engine in a so-called low speed rotation range where the cam lift is small and the valve opening / closing period is set short. On the other hand, the cam 3 formed adjacently has a larger cam lift amount and a longer valve open / close period than the cam 2 symmetrically with the cam 2 over the entire circumference. Further, it is a cam having a cam profile suitable for improving the output of the engine at a so-called medium / high speed rotation (hereinafter referred to as a high speed rotation cam).

On the other hand, of the first and second rocker arms 5, 6, the first rocker arm 5 is disposed below the low-speed rotation cam 2 formed on the camshaft 4, and the tips 5b, 5c are bifurcated. The valves are arranged so as to directly contact the heads of valve stems 8 and 9 of a valve for opening and closing a combustion chamber of an engine (not shown). The adjacent second rocker arm 6 is disposed below the high-speed rotation cam 3 formed on the camshaft 4, and the tip 6b is engaged with the tip upper surface 5d of the first rocker arm 5. It is arranged.

On the other hand, the rocker shaft 7 that rotatably supports the first and second rocker arms 5 and 6 described above has a larger diameter than other portions of the rocker shaft 7, and has an axis that is the same as that of the other portions. An eccentric large diameter portion 10 eccentric from the axis is formed, and this eccentric large diameter portion 10 is formed.
Is inserted into the support portion 6a of the second rocker arm 6. The eccentric large-diameter portion 10 is provided with an eccentric bush fitted on the rocker shaft 7.
The eccentric bush 11 includes a pin 12 for fixing the eccentric bush 11 to the rocker shaft 7. In addition, as shown in FIG. 2 which is a plan view of a main part cutaway of FIG. 1, dimensional tolerances are strictly controlled between the eccentric bush 11 and the rocker shaft 7, and the diameter is slightly smaller than the diameter of the pin 12. Holes 11a and 7a are formed.
The eccentric bush 11 and the rocker shaft 7 are fixed to each other by driving the pin 12 into the a and 7a.

In FIG. 1, reference numeral 13 denotes a screw portion for adjusting a valve clearance, and reference numeral 14 denotes a valve spring.

Next, the operation of the above-described valve train 1 will be described, and the configuration will be described in more detail.

When the rocker shaft 7 is rotated by a predetermined angle in a low rotation speed range of the four-cycle engine by a rotating means such as a servo motor or a rack and pinion (not shown) and stopped at the position shown in FIG. Surface 11 of eccentric bush 11 farthest from the axis
Since b is located at the lowermost end, only the support portion 6a of the second rocker arm 6 moves relatively downward with respect to the support portion 5a of the first rocker arm 5 and stops there.

According to such a stop position of the rocker shaft 7,
Since only the supporting portion 6a of the second rocker arm 6 moves relatively downward with respect to the supporting portion 5a of the first rocker arm 5, as shown in FIG. A peripheral surface of the high-speed rotation cam 3 formed on the camshaft 4;
A gap t is formed between the second rocker arm 6 and the peripheral surface between the high-speed rotation cam 3 and the second rocker arm 6, and the high-speed rotation cam 3 is released. 3 rotates in an idle swing state.

It goes without saying that the outer diameter and the amount of eccentricity of the eccentric bush 11 are set so as to form the above-mentioned gap t.

On the other hand, according to the stop position of the rocker shaft 7 shown in FIG. 1, the first rocker arm 5 is constantly pushed upward around the axis of the rocker shaft 7 by the urging force of the valve spring 14, The first rocker arm 5 and the peripheral surface of the low-speed rotation cam 2 are always in contact with each other. Therefore, when the camshaft 4 rotates at the stop position of the rocker shaft 7 shown in FIG. Since the stems 8, 9 move up and down following the cam profile of the cam 2 for low-speed rotation, the valve opens and closes the combustion chamber at a low speed while ensuring a suitable valve opening / closing timing and valve lift. Becomes

On the other hand, the rocker shaft 7 is rotated by a predetermined angle from the position shown in FIG. 1 in the middle and high speed range of the four-cycle engine by a rotating means such as a servo motor (not shown) described above, and the same parts as those in FIG. When stopped at the position shown in FIG. 4 indicated by the same reference numeral, the surface 11b of the eccentric bush 11 farthest from the axis of the rocker shaft 7 is located at the uppermost end, so that only the support portion 6a of the second rocker arm 6 is provided. Rises to a position equivalent to the support portion 5a of the first rocker arm 5 and stops there.

According to such a stop position of the rocker shaft 7,
Since only the supporting portion 6a of the second rocker arm 6 moves relatively upward with respect to the supporting portion 5a of the first rocker arm 5, as shown in FIG. To
The peripheral surface of the high-speed rotation cam 3 formed on the camshaft 4 comes into contact with the second rocker arm 6.

On the other hand, when the peripheral surface of the high-speed rotation cam 3 formed on the camshaft 4 shown in FIG. 4 comes into contact with the second rocker arm 6, the high-speed rotation cam 3 becomes the lower-speed rotation cam. The second rocker arm 6 is formed so that the cam lift is larger than that of the second rocker arm 6.
6b is disposed so as to engage with the upper surface 5d of the tip of the first rocker arm 5, so that when the camshaft 4 rotates at the stop position of the rocker shaft 7 shown in FIG. The cam 2 rotates in an idling state, and the first rocker arm 5 operates by being pushed by the tip 6b of the second rocker arm 6, so that the valve stems 8, 9 of the valves for opening and closing the combustion chamber are rotated at the high speed. The valve moves up and down following the cam profile of the cam 3, so that the valve opens and closes the combustion chamber at a high speed while securing a suitable valve opening / closing timing and valve lift.

When the high-speed rotation cam 3 shown in FIG. 3 is not operating, the second rocker arm 6 has no constraint, so that the rocker shaft 7 moves up and down with the tip 5d of the first rocker arm 5 which moves up and down. It may be affected by factors such as collisions, which may be a source of noise.
As shown in FIG. 6 in which the same parts as those in the drawing are denoted by the same reference numerals, when a coil spring 20 is interposed between a distal end 6b of the second rocker arm 6 and a distal end 5d of the first rocker arm 5, they are connected to each other. The second rocker arm 6 moves up and down in synchronism with the movement of the first rocker arm 5, so that it is possible to eliminate such a flutter of the second rocker arm 6.

In order to eliminate the protrusion of the second rocker arm 6 when the high-speed rotation cam 3 is not operated, the tips 21a and 21b are bent downward in opposite directions as shown in the conceptual perspective view of FIG. A coil spring 21 is used, and this coil spring 21 is attached to the rocker shaft 7 between the first rocker arm 5 and the second rocker arm 6 as shown in FIG. Fitting, the tip
The first and second rocker arms 5 and 6 may be sandwiched between 21a and 21b so that the movement of the first rocker arm 5 is synchronized with the movement of the second rocker arm 6.

In the above embodiment, in forming the eccentric large diameter portion 10, as shown in FIG. 2, an eccentric bush 11 and a pin 12 are used, and the pin 12 is formed with holes 11a, 7a having tightly controlled dimensional tolerances. The eccentric bush 11 and the rocker shaft 7 are fixed by being pressed into the inside, but the present invention is not limited to the above-described embodiment, and the same parts as those in FIG. As shown in the figure, each hole 11a, 7a formed in the eccentric bush 11 and the rocker shaft 7 is formed as a so-called fool hole loose in dimensional tolerance, and a pin 12 is slidably fitted in the holes 11a, 7a. After the insertion, all of the eccentric bush 11 is inserted into the support portion 6a of the second rocker arm 6, and further the bearing portions 30, 31 for rotatably supporting the rocker shaft 7 are provided. A coil-shaped thrust spring 32 is disposed on the rocker shaft 7 on the side of the bearing 31, and the entire first and second rocker arms 5, 6 are moved to the other side (the second rocker arm 6) by the urging force of the thrust spring 32. Side), the positioning is performed by pressing against the side of the bearing portion 30 so that the pin 12 is prevented from being removed from the inner peripheral wall of the support portion 6a of the second rocker arm 6 and the eccentric shaft 11 and the rocker shaft 7 are fastened. It may be.

Note that, as in the embodiment shown in FIG. 9, each hole 11a formed in the eccentric bush 11 and the rocker shaft 7,
7a is formed as a so-called fool hole whose dimensional tolerance is loose, and the pin 12 is slidably inserted into the holes 11a, 7a. Then, all of the eccentric bush 11 is connected to the second rocker arm. 6 can be inserted into the supporting portion 6a of the supporting member 6 and further positioned by the thrust spring 32, and the pin 12 can be prevented from being pulled out by the inner peripheral wall of the supporting portion 6a. The assembly and disassembly work of the device 1 is performed, and the holes 11a,
Since 7a may be a so-called fool hole in which the dimensional tolerance is loosely controlled, the dimensional tolerance can be easily controlled, so that the manufacturing process of the valve gear is further simplified.

In each of the above embodiments, the valve train 1 according to the present invention is described.
Is applied to a so-called four-valve engine having two valves on each of the intake and exhaust sides. However, the present invention is not limited to the above embodiment, and one valve is provided on each of the intake and exhaust sides. The valve train 1 according to the present invention may be applied to the intake / exhaust side of a so-called two-valve engine having the following.

Further, in the above embodiment, the eccentric large diameter portion 10 is constituted by the eccentric bush 11 and the pin 12, but the present invention is not limited to the above embodiment, and the eccentric large diameter portion 10 is formed integrally with the rocker shaft 7. You may.

〔The invention's effect〕

As described above, in the valve gear according to the present invention, the cam profile of the cam that operates the valve according to each rotation range of the engine is selected from two types according to the engine speed, and the opening / closing timing of each valve and Since the valve lift can be changed to an optimum value according to the engine speed range, the output of a four-stroke engine can be improved in a wide speed range from low to medium and high speed ranges. Can be done.

Further, in the valve gear according to the present invention, since the rotary motion of the rocker shaft when the cam is selected is converted into the vertical motion of the second rocker arm by the eccentric large diameter portion, a large stress is applied to each portion when the cam is selected. Therefore, the selection of the cam is smoothly performed.

Furthermore, since the valve gear of the present invention is configured without making a significant change to the conventional valve gear, it can be mounted by performing the minimum processing on the cylinder head having the conventional shape. In practicing the present invention, there is also an advantageous effect that an increase in production cost can be minimized.

[Brief description of the drawings]

FIG. 1 is a conceptual perspective view of a valve train according to the present invention, and FIG.
Fig. 3 is a fragmentary plan view of Fig. 1; Fig. 3 is a sectional side view of main parts of Fig. 1; Fig. 4 is a conceptual perspective view showing the operation of the valve train according to the present invention. Figs. 4 is a cross-sectional view of a main part, FIG. 6 is a cross-sectional view of a main part showing a spring connecting the first and second rocker arms, and FIG. 7 is a cross-section of the first and second rocker arms. FIG. 8 is a conceptual perspective view showing another embodiment of the spring, FIG. 8 is a fragmentary plan view showing a state where the spring shown in FIG. 7 is mounted, and FIG. 9 is another embodiment of the valve gear according to the present invention. FIG. 1. Valve operating device, 2, 3 ... Cam, 4 ... Cam shaft,
5 first rocker arm, 6 second rocker arm, 5a, 6a support, 7 rocker shaft, 8, 9
… Valve (valve stem), 10… Eccentric large diameter part, 11… Eccentric bush, 12… Pin.

Claims (2)

(57) [Claims] 1. A camshaft in which two types of cams having different cam profiles are formed adjacent to each other, and a cam lift of one cam is larger than a cam lift of the other cam; and a cam formed on the cam shaft. A first rocker arm disposed below a cam having a small cam lift and directly abutting on a valve head for opening and closing the combustion chamber; and a cam having a large cam lift among the cams formed on the cam shaft. A second rocker arm disposed on the first rocker arm and engaged with the upper surface of the first rocker arm, rotatably supported and fitted into each of the support portions of the first and second rocker arms. In addition, the portion to be inserted into the support portion of the second rocker arm has a diameter larger than that of the other portion, and the axis of which is eccentric from the axis of the other portion. A rocker shaft having a trick large-diameter portion formed thereon, and by rotating the rocker shaft by a predetermined angle, the eccentric large-diameter portion changes the support portion of the second rocker arm to the support portion of the first rocker arm. Relative to the first rocker arm by releasing the contact between the cam having a large cam lift and the second rocker arm and bringing the cam having a small cam lift into contact with the first rocker arm. Operating the valve by following the cam profile of the cam having the small cam lift amount, and rotating the rocker shaft by a predetermined angle, thereby allowing the support portion of the second rocker arm to be moved by the eccentric large diameter portion to the second position. 1 to the same position as the supporting portion of the rocker arm, and reduce the cam lift amount. The contact between the cam and the first rocker arm is released to bring the cam with the large cam lift into contact with the second rocker arm, and the valve follows the cam profile of the cam with the large cam lift. A valve train for a four-stroke engine, wherein the valve train is operated by being operated. 2. An eccentric bush according to claim 1, wherein said eccentric large-diameter portion is pivotally supported by said rocker shaft and inserted into a support portion of said second rocker arm. When slidably fitted into the holes formed in the eccentric bush and the rocker shaft, respectively, and fitted into the support of the second rocker arm, the inner peripheral wall of the support of the second rocker arm is used. The rocker shaft has a pin whose movement is restricted, and the rocker shaft has a thrust spring for simultaneously urging and positioning the first rocker arm and the second rocker arm toward the second rocker arm. The valve train of a four-stroke engine.